Microbial regulation mechanisms of soil organic carbon sequestration by biochar application

The application of biochar to agricultural soils is a promising strategy for reducing greenhouse gas emissions and enhancing carbon sequestration. However, the microbially mediated mechanisms by which biochar influences soil carbon cycling remain unclear. Through a meta-analysis, we evaluated the responses of soil organic carbon (SOC) and microbial communities to biochar application, aiming to elucidate microbial regulatory roles in biochar-induced carbon sequestration processes. Our results demonstrated that biochar significantly increased all SOC fractions (mean increase: 52.4%), along with concurrent increases in soil total nitrogen (17.6%) and pH (4.1%). Divergent ecological strategies among bacterial phyla drove different SOC responses. When broad-niche phyla functioned as the sensitive (Proteobacteria) or dominant (Actinobacteria) taxa under our sensitivity classification, they facilitated the greatest SOC increases (68.6% and 52.4%, respectively), exceeding the overall mean. Oligotrophic phyla (Acidobacteria and Chloroflexi) domination resulted in limited SOC gains (47.3% and 28.8%, respectively). Broad-niche phyla exhibited enhanced organic carbon decomposition and nutrient utilization, promoting SOC accumulation. In contrast, oligotrophic phyla, typically adapted to low-nutrient environments, demonstrated suboptimal carbon utilization, possibly even accelerating SOC decomposition, ultimately reducing the net carbon sequestration. Overall, we revealed the microbial regulatory mechanisms governing biochar-induced carbon sequestration, providing a basis for evaluating biochar carbon sequestration based on microbial communities. Graphical Abstract